1. The Cement Concrete and Existent Polymer Modified Cement Concrete
Cement concrete is a commonly known and extensively applied construction material. However, because cement concrete material has its own unconquerable weaknesses such as large shrinkage in its early setting, initial inner defections, high brittleness and easy cracking. Modification of cement concrete has been under study and research for a long time.
Years ago a type of polymer modified cement concrete emerged. In the polymer modified cement concrete polymer or polymer emulsion is utilized to modify cement. Polymer cement grout (or slurry) or polymer emulsion cement grout is applied as a binder material to bond aggregates (such as broken stones) and sand together. Consequently the compressive strength, tensile strength and impact toughness of the polymer modified cement concrete are greatly improved with features of high corrosion resistance and outstanding flexibility. So it is applied extensively.
Currently polymer modified cement concrete is primarily applied as a material in mending work, decoration or house floor paving. In structure engineering polymer modified cement concrete is also accidentally applied to road pavement and bridge deck. Generally there are two construction technologies in polymer modified cement concrete work: I. If the aggregates in the concrete has relatively large particle sizes the similar construction technology with that for common cement concrete work is applied; The polymer modified cement concrete is required to have enough fluidity, a general slump range of 3-5 cm; After vibration to high density the polymer modified cement concrete is applied to floor with a paving thickness of 2-4 cm. II. If the aggregates in concrete has relatively small particle sizes greater fluidity of the polymer modified cement concrete is required (also known as polymer cement mortar) and brushing method is applied to spread the mortar onto the surface of a structure layer by layer with an overall thickness of 0.5-2 cm, such a construction method is generally suitable for mending and repairing and decorating.
In unit volume of the existent dense polymer modified cement concrete consumption quantity of polymer is rather large thus a very high construction cost is inevitable. In addition the thickness formed in one layer of brushing is rather small (no greater than 1 cm) and therefore the above second type of construction technology generally is labor-costly and not suitable for large-area construction or big-thickness paving (e.g. above 4 cm).
2. Road Paving and Other Paving Engineering
There are two primary types of pavement structures for highway, namely cement concrete pavement and asphalt concrete pavement. Cement concrete pavement is generally known as rigid pavement while asphalt concrete pavement is known as flexible pavement. The cement concrete pavement slab has greater rigidity, higher strength and larger elasticity modulus than those of the underlying base course and foundation. “Rigidity” is typical of the cement concrete pavement. The asphalt concrete pavement bears elasticity modus more nearer to that of the base course, and has a better flexibility and therefore is easier to adapt to the deformation of the base course and foundation. “Flexibility” is typical of the asphalt concrete pavement.
The cement concrete pavement involves in various types such as plain cement concrete pavement, reinforced concrete pavement, continuously reinforced concrete pavement, prestressed concrete pavement, prefabricated concrete pavement and steel fiber reinforced concrete pavement. Currently, cast-in-place plain cement concrete pavement is most extensively applied. The plain cement concrete pavement is of such advantages as convenient availability of source materials, simple construction method, high strength, sound stability and high durability. But it is also of such weaknesses as poor riding comfort, poor adaptability to base course deformation and easily damaged joints, it is hard to repair and restore after failure. In addition the plain cement concrete pavement slab needs a thickness generally over 20 cm.
The asphalt concrete pavement is formed through bonding the well graded aggregates by asphalt as a binder material. The asphalt pavement course may consist of one, two or three layers of asphalt concrete. In design of each layer of asphalt concrete factors of layer thickness, layer position, temperature, precipitation and traffic volume shall be considered. Though asphalt concrete pavement bears such advantages of even and smooth surface, no joint, comfortable riding, wearability, low vibration, low noise level and convenient maintenance, its construction procedure is relatively difficult and its water resistance, temperature resistance and aging resistance are poor, that may cause failure forms such as rutting, crumbling and reflective cracking, etc. Thickness needed for the asphalt concrete pavement is generally smaller than that for the plain cement concrete pavement.
3. Existent Problems
Dense concrete is required in existent common polymer modified cement concrete pavement, plain cement concrete pavement and rolled and compacted cement concrete pavement. Quality control of the pavement construction strictly rules out voids and pores in the concrete.
Dense concrete is also required in existent common asphalt concrete pavement. Failure forms such as rutting and cracking often occur due to low strength, poor aging resistance and high temperature sensibility of the dense asphalt concrete.
The special asphalt open grade friction concrete (OGFC) contains voids in interior and is of such features as water permeability and noise reduction. However, voids in the asphalt material as binding matrix bring much lower concrete strength than that of dense type asphalt concrete, thus structural damages occur more easily in OGFC pavement, and OGFC has not yet been widely applied to highway for heavy duty traffic.